2. Field of the Invention.
The present invention relates to a control lever apparatus and an actuator operation apparatus which are for use in construction equipment such as a crane. More particularly, the present invention is concerned with a control lever apparatus having a detent device which is capable of holding the lever at a switching operation position and also relates to an actuator operation apparatus having a reaction force device capable of imparting to the lever an operation reaction force of a level corresponding to the load pressure acting on the actuator.
2. Discussion of the Background
Japanese Utility Model Laid-Open No. 55-14199 discloses an operation apparatus which is provided with a reaction force device which imparts an operation reaction force of a level corresponding to the load on a hydraulic motor of a crane for lifting and lowering a load in order to enable the operator to sense the movement of the load handled by the crane.
On the other hand, Japanese Utility Model Laid-Open Publication Nos. 61-190620 and 190621 disclose a control lever apparatus having a detent device which is composed of a potentiometer and a torque motor for holding the control lever at a desired operational position.
The operation apparatus disclosed in Japanese Utility Model Laid-Open No. 55-14199 has a pilot lever operated through a lever. The pilot valve produces a pilot pressure of a level corresponding to the operation of the lever, so that a pilot-type control valve is switched by the pilot pressure. As a result of switching of the control valve, a pressurized fluid is supplied to a hydraulic motor for operating a winch so as to actuate the hydraulic motor. The hydraulic motor in turn drives a winch drum connected to the rotor of the hydraulic motor so as to lift or lower a load. Meanwhile, the hydraulic load pressure acting in the motor is introduced to a chamber in a reaction force cylinder, through conduits communicating with ports on both sides of the hydraulic motor and through a pilot conduit. The reaction force cylinder is connected to the pilot valve. The load pressure introduced into the above-mentioned chamber acts to push a piston in the reaction force cylinder and a rod connected to the piston. The rod is brought into contact with a cam connected to the lever so as to produce a force which acts to return the lever to the neutral position, i.e., an operation reaction force. This operation reaction force is proportional to the load pressure acting in the hydraulic motor, so that the operator operating the lever can sense the reactive force proportional to the load pressure in the hydraulic motor. The operator therefore can feel the movement of the load through sensing the change in the load pressure.
In this operation apparatus, however, the lever is returned to the neutral position unless the operator holds it against the reaction force. Therefore, when lifting or lowering of the load is continued for a time period, the operator is obliged to hold the lever at an operative position against the reaction force.
On the other hand, the detent device for a control lever disclosed in Japanese Utility Model Laid-Open Publication Nos. 61-190620 and 61-190621 has a potentiometer connected to a pivot shaft of the lever and a torque motor. The angle of rotation of the pivot shaft, corresponding to the amount of operation of the control lever, is converted by the potentiometer into an electrical signal. This electrical signal, representing the detected amount of operation of the control lever, is compared with values set in a setting device in which lever detent positions are set. The lever is provided with a detent canceling switch. When the detent canceling switch is off while the lever is in the detent position, a position holding signal is delivered to the torque motor so that the torque motor produces a torque necessary for holding the lever at the detent position. When the lever is set at a position other than a detent position while the detent canceling switch if off, a reaction force signal is delivered to the torque motor so that the torque motor imparts an operational reaction force to the lever When the detent canceling switch is on, the reaction force signal is generated over the entire range of the lever position so that the torque motor imparts a predetermined level of reaction force to the lever regardless of whether or not the lever is in a detent position.
The detent device of the control lever of the type mentioned above controls the torque motor in accordance with an analog detection signal derived from the potentiometer such that the torque motor controls the force on the lever, i.e., the force for holding the lever at a detent position and the operational reaction force Thus, the operation reactive fore is controlled in accordance with the angle or amount of operation of the lever, regardless of the load pressure in the actuator In addition, holding of the lever at a detent position tends to cause hunting of the lever at the detent position due to fluctuation in the response of the torque motor.